1. Field of the Invention
The present invention relates generally to an optical disk system for playing back signals from a recorded media, and more particularly to a video disk apparatus which provides uninterrupted continuous playback of a dual-sided optical disk during the period of switching from one side of the disk to the other side of the disk.
2. Description of the Related Art
Generally, optical disks have tracks that can record and play back various types of data. Common optical disks include compact disks (CDs), CD-ROMs, digital video disks or digital versatile disks (DVDs), or other similar disks. Some optical disks, such as DVDs, may be either single-sided or dual sided, i.e., data may be stored on only one or both sides of the disk.
In the situation where data is stored on both sides of the optical disk, the optical disk must be “flipped” from one side to the other in order to read data from both sides of the disk, or the playback apparatus must be capable of reading both sides of the disk without the disk being “flipped” over. Generally, a conventional optical disk recording and playback device uses one optical pickup to record or playback data on the tracks of a side of the disk adjacent to the optical pickup. Upon completion of the recording and playback of data on the side of the disk adjacent to the optical pickup, the disk is flipped, either by human manual intervention or an automatic changing device, to access the data from the other side of the disk. The manual flipping of the disk may require that the disk be taken out of the optical disk recording and playback device and then reinserted back into the optical disk recording and playback device.
In the case of an optical disk recording and playback device which has an automatic changing device, a rotatable transfer mechanism may be used to load a disk to an optical reader. The optical pickup is located within the optical reader to access the data on the side of the disk facing the optical pickup. When the first side of the disk has been read by the optical pickup, the disk will be transferred from the optical reader back into the transfer mechanism, the transfer mechanism rotated about its axis, and the disk reinserted back into the optical reader with the second side facing the optical pickup.
However, there are limitations with respect to the operation of devices in which the disk is flipped, either manually or automatically. The reproduction of the video signals must be stopped while the disk is being flipped until the data on the second side of the disk can be accessed. As a result, a video picture is stopped on a screen for the period of time required for the disk to be flipped, thus interrupting a movie or game program stored on the disk.
Alternatively, devices have been developed in which the data on both sides of an optical disk can be continuously accessed without the need for manually or automatically flipping the disk. Such devices may employ either one or two optical pickups.
An example of a continuous both-side playback device utilizing a single pickup is illustrated in U.S. Pat. No. 5,257,111. The single pickup is adapted to read the video signals recorded on both sides of the video disk by moving along a U-shaped track from the center of the top side of the disk to the center of the bottom side of the disk around the edge of the disk. However, there are limitations associated with this type of device similar to those in which the disk is flipped. Namely, the reproduction of the of the video signals must be stopped during the time the second side of the disk is being accessed, i.e., while the pickup moves from the outer circumference of the lower side of the video disk to the inner circumference of the upper side of the video disk to read the video signals recorded on the upper side of the video disk after reading all the video signals recorded on the lower side of the video disk. As a result, a video picture is stopped on a screen for about 10–15 seconds, thus interrupting the movie or game program stored on the disk.
An example of a continuous both-side playback device utilizing two pickups is illustrated in U.S. Pat. No. 5,448,373. A first pickup is provided to read data from the top side of the disk, and a second pickup is provided to read the data from the lower side of the disk, thus removing the necessity for flipping the disk. During operation, the video disk is rotated in a counter-clockwise direction to read the video signals recorded on the lower side of the video disk. The rotation is then halted and reversed to a clockwise direction to read the video signals recorded on the upper side of the video disk. To overcome the problem of the time required to reverse the rotation of the video disk from the counter-clockwise direction to the clockwise direction (approximately 4–6 seconds) and the resulting stoppage of the video picture on the screen, both sides of the video disk are read and stored in a memory. The contents of the memory are then output so that the video signals from both sides of the disk can be successively reproduced with no discontinuity. However, this type of device requires an extensive amount of memory space to store the entire contents of both sides of the disk. The extensive amount of memory required results in both increased costs for the device and an increase in physical size of the device.
Therefore, although the conventional optical disk systems are capable of continuous playback of dual-sided optical disks, they do not provide an apparatus or method for uninterrupted continuous playback without utilizing an extensive amount of memory to store the entire data contents of both sides of the disk before playback. Thus, there exists a need for an optical disk system that is capable of continuously playing back signals from a double-sided recorded media without interruption when the side being read is switched, without requiring an extensive amount of memory space.